Azure website clarity regarding the instances, are these instances running on multiple machine like a web server farm environment where one client request (session) can be server by different server in the farm.
Issue with server farm asp.net application is that we can loose session variable if that is the case, for this issue to get around we add machine key in web.config that assure client session will always be server by same server so there wont be any lose of session variable.
How does Azure instance work. doesnt it mean we can have 10 websites under same plan let ex s1 Standard.
I am hosting asp.net webform based website on Azure I am confused how exactly instance work. there are lot of article on internet to create confusion.
The thing with PaaS is that you don't have to care about that. If you have a statefull site, you can use the ARR Affinity setting to ensure a client gets always to the same instance:
Adding to Martin Brandl's answer.
An App Service Plan can have multiple instances. These instances run all of the apps in that plan. So it is pretty much like a classic web farm. Except it is way easier to manage.
There is a better way of keeping session information in a web farm rather than relying on sticky sessions with ARR Affinity. Put the session data in a central place. For that you can use Azure Redis Cache or SQL Database. There are ready-made session state providers for these that you can just plug in to an ASP.NET application. That way your session state is not stored on the instances, so you don't need to care if clients hit the same server.
The problem I have with ARR Affinity, is that Azure does not guarantee your instances will remain running. A hardware failure could bring one down and you lose a part of your session data. If you use auto-scale, same thing.
Related
I read that when using Session objects in an ASP.NET web app hosted in Azure, if the request is handled by a different (virtual) machine, the app cannot see Session variables of another virtual machine (obviously), so it is recommended to use Azure Caching Service.
Just to understand:
can these 'virtual machine switches' happen in 'normal' web sites too?
I mean: if I don't configure redundancy (i.e. multiple instances) do I have the risk to 'not see' session variables just the same?
Thanks in advance.
AB
If you are using Azure Web Sites with a single instance, then you can technically use in-process session storage since all requests are handled by the same instance. Even when using multiple instances in Azure Web Sites, the default behaviour is to use ARR with "sticky" load-balancing, so that all requests for a particular client are routed to the same instance.
However, there are still times when all in-process session data may be lost. If an instance fails, then the site will be quickly transferred to another instance, and any in-memory (or on-disk) data will be lost. For that reason it is better to use some form of separate, persistent storage such as caching, table storage or a SQL database for your session data if it is in any way essential. I believe all the ASP.NET session providers maintain an in-process cache of the underlying store for performance reasons anyway.
If you are using a Cloud Service to run your site, then all requests are load-balanced between all available instances, so separate session storage is essential.
Basically my question is i have a website which was developed around 3 years ago, while development it was proposed that this site will be used by few people on internet.
But now it seems like many users are accessing the website. So we have planned to create a Web sever Farm where we have multiple servers for our website.
major problem in development is old website used InProc Session state and now since we are upgrading to multiple servers we want to change InProc to Outproc i.e StateServer Session State.
Can you guide me on this upgrade and how can it be achieved in simple and easy way rather than changing the coding on each pages wherever sessions are used.
What you going to have here is that you move your site to many web servers and the actual issue here is "how to keep the same state for each user regarding the server".
There are two options.
First option is to setup the router that split the users to the server, to use the "Sticky option", meaning that each user is stick for his session to one server, and one only. In this case it did not matter if you use inproc or sql server session, as long as the router make good job. This is the case of course that you do not use any other database for common data.
Second option is to use an sql server and move the session to the server, but here the server must be on one server and the others server's gets his session data from this one. Also you setup on web.config the same key machine for all web servers.
So for this case you need.
To setup a common/shared SQL server on one server
To install on this the session database (actually run a script from asp.net)
Setup the web.config to use this database as session
Setup the web.config to have the same machine key.
In the case that you use a database for other data, then you place this database together with the session database, and you make a share connect to that database also. The point here is that the data must be live on one computer, and the other computers connect to this main one for the data.
I want to know in which situation i am use this mode ?
Sql Server Mode is one way to handle sessions inside of a web farm for example. If you were to use in proc session state inside of a web farm, you would not be able to share a session over many boxes. Using Sql Server for the storage of the session means that you can load balance your users over the servers inside of the web farm and the session can be retrieved externally, inside of SQL Server. So one web server would allow you to use in proc session state. With many servers you need to store the session state in a common place so all web servers can see the same one.
It's mainly used when you want to use your app on a web farm, web garden, or cluster. Since page requests can come from multiple processes or computers, you can't use an in-process session state provider.
http://idunno.org/articles/277.aspx
Greetings,
What do I have to consider when you are coding an ASP .Net website in regards to if the application will run in a environment where there is a load balancer for the IIS?
All user sessions are running by them self with no shared data between sessions. Single connections to MSSQL. Images and files for download will be hosted on one single server.
Windows Server 2008's, C# and .Net 4.0.
The most obvious item is session state. If you are load balancing, multiple requests from the same user may move between servers. The default session provider for ASP.NET (in-proc) doesn't support this (the user would get a new session each time they moved). The easiest solutions are to move to a ASP.NET state server or SQL Server sessions.
FYI: Both of these solutions require that everything that you put into Session be [Serializable]. The in-proc provider doesn't have this requirement, so you may see some runtime errors and need to modify your code when you change providers.
You're going to need to move your session state into the session state service. Avoid keeping objects in session...if you must keep an object in session, make sure it's marked with the Serializable attribute (this is how it is stored, by serialization).
In general, avoid using Sessions. Keep in mind that ASP.Net Session != FormAuthentication. Chances are that your database will be a bottleneck long before the web server, depending on the nature of the application.
We have 5 balanced web servers with various websites.
What I am trying to achieve is to ensure a single login.
i.e. the same user account cannot login to the same website more than once at any given time.
The method i'm considering for solving this, is to share session amongst the servers so I can control which session is assigned to which account. I can then have control over my logins. If a user logs in and there is already a session assigned to their user account, I can just expire the first session or reject the login.
I don't want to lose the benefit of the balanced servers, so using a single Sql Server as my session state server, or a single server to handle login is not an option.
Is distributed session (something like Scaleout Sofware) the correct approach to achieve this?
Or is there another mechanism to handle single login that i'm blissfully unaware of?
You have two set of problems here:
1) Allowing just one connected user in a web farm scenario
2) Detecting user logoff
To solve the first the only solution is a central storage for some kind of user state, using a central server to store the ASP.Net session or some other kind of centralized user state. This central storage can be SQL Server using the native management of session state (btw also Oracle, from Oracle 11, can support session storage), the AspState service or an external solution, like ScaleOut (as you said) or its open source alternative memcached (see https://sourceforge.net/projects/memcacheddotnet/). Or you can design a simple centralized web service that check active logins against a SQL Server database, this way you can also quickly create reporting tools about logged on users and so on.
Real problem, in my opinion, lies in the second part, that you need to maintain the different "wrong logoff" scenarios that are available in a web world (like closing the browser due to a crash or shutting down applications without logging off), giving you application some way to gracefully work with user that has an old session enabled (as you said simply expiring the first session can work).
Keep also in mind that using a state server like SQL server will not make you loose the balanced servers, if's the way of working to have a web farm environmet and sharing session, only problem lies in performance (if session state become large) and the cost involved in using SQL Server if you do not already have the proper license.